Typically, pigments having fine particle diameters tend to have a strong cohesive force between pigment particles and thus are liable to disperse insufficiently in media, such as organic solvent and molten resins. The insufficient dispersibility of pigments results in low tinting strength of pigments.
Thus, it is reported that a dispersant to disperse a pigment is used together with the pigment in order to improve the dispersibility of the pigment. In particular, a variety of dispersants for color toners of yellow, magenta, cyan, black, and so forth are reported in order to improve the dispersibility of a pigment in toner particles.
Specifically, PTL 1 discloses that in order to improve the dispersibility of an azo-based pigment in a yellow toner, a compound having an azo skeleton structure is used as a dispersant.
PTL 2 discloses that in order to improve the dispersibility of a magenta pigment in a magenta toner, a specific polyester-based dispersant is used as a dispersant.
PTL 3 discloses that in order to improve the dispersibility of a phthalocyanine pigment in a cyan toner, a polymer containing sodium styrenesulfonate serving as a monomer unit is used as a dispersant.
PTL 4 discloses that in order to improve the dispersibility of carbon black in a black toner, a copolymer composed of a styrene-based monomer and an acrylate-based (or methacrylate-based) monomer is used as a dispersant.